JP2001-289014A (document 1) describes a fluid supply apparatus for supplying a fluid from a fluid storage portion to a fluid supplied portion. In the document 1, a valve timing control apparatus for an engine of a vehicle is taken as an example of the fluid supplied portion. The valve timing control apparatus controls a rotational phase angle of a camshaft, which operates an intake/exhaust valve of an engine, relative to an engine crankshaft for controlling intake/exhaust valve timing on the basis of the amount of a fluid supplied by the fluid supply apparatus. In the case where a fluid pressure rises because of counter force from the cam or the like, the fluid tends to leak into a lubrication passage for a crankshaft, a connecting rod, a piston, or the like, or the fluid tends to flow back to an oil pan side. As a result, the valve timing control apparatus is lead to a deficiency in the fluid. For overcoming this, according to the document 1, a check valve is provided for preventing the fluid from flowing back to the fluid storage portion side from the fluid supplied portion side. By doing so, even when the fluid pressure rises in the valve timing control apparatus, a probability of a phenomenon in which the fluid leaks into the lubrication passage or a phenomenon in which the fluid flows back to the oil pan side can be reduced.
However, according to the document 1, because the check valve is provided in a fluid supply passage between the fluid supplied portion and the fluid storage portion, when a temperature of the fluid is low and viscosity of the fluid is high, for example, when an engine starts operation while the engine is cold, pass resistance of the fluid rises in the fluid supply passage. Accordingly, there are adverse effects that the fluid cannot sufficiently supplied to the fluid supplied portion from the fluid storage portion, and that the valve timing control apparatus (fluid supplied portion) cannot start operation properly.
A need thus exists for a fluid supply apparatus, which can supply a fluid to a fluid supplied portion with reliability even when viscosity of the fluid is relatively high. The present invention has been made in view of the above circumstances and provides such a fluid supply apparatus.